In the early development of rifles, and the like, the barrels of such weapons were usually of such a character that the internal bore of the barrel was essentially smooth. Such weapons were in use for many years with black powder, a forerunner of modern day smokeless powders. One early attempt at improving the accuracy of such barrels was disclosed U.S. Pat. No. 37,193 issued to C. R. Alsop on Dec. 16, 1862. This patent sought to improve the accuracy of smooth-bore gun barrels by attaching a rifled section to the muzzle end of a conventional smooth-bore gun barrel. The rifled section that was added was generally two to three inches in length, and the direction of twist of the rifling was opposite to that of the threads which connected the rifled section to the smooth-bore barrel. By such a technique, the projectile when it entered the rifled section of the barrel would have a tendency to tighten the threaded connection of the extension on the barrel.
The Alsop patent recognized that the rifling imparted a significant degree of friction to the projectile, but it found that placing the beginning point of the rifling far enough down the barrel away from the breech end, the friction was said to be overcome by the accumulated momentum of the projectile.
This patent also suggested a gradual reduction in diameter of the bore of the barrel progressing away from the breech end into the rifled portion.
However, the early teachings of this Alsop patent could not be carried forward into modern day technology because of the great differences in projectiles and in the powders used in the ammunition for such gun barrels. Were this technology to be used with modern day ammunition, an explosion of the barrel would be the likely result.
As a consequence, smooth-bore rifles essentially disappeared, and the smooth-bore technology currently is primarily only used in antique type or replica weapons using black powder, or shot guns which use a smooth-bore with a constriction or choke at the end of the barrel to contain a pattern of shot in the cartridge, as opposed to a single projectile.
Shotguns are also occasionally used with a single projectile or "slug", but the accuracy of such ammunition is relatively poor. This accuracy is improved, however, by using a so-called "rifled slug" which has rifling grooves on the outer surface of the slug to impart a spin to the projectile. While being an improvement, this does not achieve the accuracy of a rifled barrel.
It has long been known that the presence of rifling grooves in a gun barrel imparts substantial friction to the projectile. While this in itself would be detrimental to long range accuracy, the development of modern day gun powders has in effect overcome the disadvantages of the friction of rifling to the extent that the rifling is currently used in most all gun barrels, for the rotary motion or spin it imparts to the projectile to stabilize the projectile in flight which in turn improves the accuracy of the weapon.
More recently, U.S. Pat. No. 3,525,172 to R. L. Marshall et al, issued on Aug. 25, 1970, combined the technologies of smooth-bore barrel design and rifled barrel design to obtain an improved accuracy using modern day ammunition and powders. This patent discloses an improved gun barrel wherein the rifling in the barrel extends from the breech end of the barrel to the point along the length of the barrel at which the gas pressure in the barrel reaches a maximum, and from that point forward towards the muzzle end of the barrel, the barrel has a smooth, unrifled bore. In this manner, improved velocity and accuracy of the projectile could be obtained.
The improvements in applications Ser. No.'s 131,318 and 516,230 related to the improvements over the earlier Marshall et al patent whereby the end portion of the barrel, i.e. the smooth-bore section of the barrel was connected to the rifle portion of the barrel by a threaded, releasable connection between the two barrel sections.
The particular threaded connection between the two barrel sections enabled easier replacement of either barrel section after wear, and additionally provided sealing surfaces between the two sections of the barrel to minimize or eliminate the loss of gas pressure at the transition between the two barrel sections.
One of the disadvantages of the Marshall et al patent was the difficulty in producing a barrel having the rifling along one portion and a smooth-bore along the other portion of the bore. It is very difficult to accurately control the internal dimensions of such a barrel which was produced from a single piece of stock. Further, the concentricity of the bore with respect to the barrel was jeopardized, and fluctuations in the concentricity were significant, such that heat build-up would cause thermal distortion of the barrel resulting in reduced accuracy.
Moreover, it has been found that simply the provision of a smooth-bore section at the end of the rifled portion of the barrel does not necessarily result in the improved benefits of the weapon. The bore itself must be accurately machined with respect to the characteristics of the rifling section of the barrel, and the caliber of the gun.
Accordingly, a primary object of this invention is to provide an improved gun barrel combining smooth-bore and rifled-bore technology.
Still another object of this invention is to provide an improved gun barrel in which the smooth-bore section at the muzzle end of the gun is configured in a predetermined manner in relation to the rifled section of the barrel.
Still another object of this invention is to provide a two piece gun barrel wherein a smooth-bore section at the muzzle end is threadedly connected to a rifled barrel section at the breech end.
Still a further object of this invention is to provide an improved barrel construction wherein the diameter of the bore in the smooth-bore section is intermediate the diameters of the lands and the grooves in the rifled section.
These and other objects in advantages of this invention will become apparent when considered in light of the following description and claims when taken together with the accompanying drawings.